Re: The Age of Electric Vehicles
Posted: Wed Jan 12, 2022 9:19 am
For an ICE, trip distance is also important, because you spend the first ten minutes heating half a tonne of metal up to 90 degrees.
The traditional number is that cars are most efficient at around 80-90 km/h. The engine itself has a sweet spot, and then you need to get into a gear which is as high as you can sweetly run. But you can't just put in ever higher gears and get even more efficient, because air resistance goes up.Gfamily wrote: ↑Wed Jan 12, 2022 12:35 amIf a motorway has a 50mph limit because of roadworks, our average mph goes up to c50/52 mpg rather than the c46mpg we average when travelling at our usual 66/70mph.Bird on a Fire wrote: ↑Wed Jan 12, 2022 12:24 amI often wonder what's the most efficient speed to drive at. If I bumble along at a solid 90km/h it maybe adds a few minutes to my commute compared with 120km/h, but it keeps the revs so much lower I assume I'm saving fuel.
Presumably you can also extend an EV's range by driving efficiently? I've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
ETA: air resistance goes as 4th power of speed (i think), so high speeds can make a big difference
Same for an EV, because you spend the first few minutes heating half a tonne of batteries up to about 15 degrees.
True, I've done that trip twice in the whole time I've owned the car. Before the Event I would fill up about once a month, but there was a phase when it was nearly twice a month because I was going to Milan a lot in the evenings. So 300-500 km a month, Milan is a 100 km round trip. At the end of October I went to (somewhere near) Turin, and I can get there (and use the car a bit there) and back (~350 km).bjn wrote: ↑Wed Jan 12, 2022 9:09 amAverage car usage in the UK seems to be roughly 10 miles/day. That will be some distribution with road warriors driving a million miles/day at one end and OAP's driving a mile once a month to the bingo hall down the road.
At 3.5 miles/kWh that translates to an average energy consumption of 3kWh/day, which is less than half an hour in a 7kW charger. Say you charge once a week, that's less than four hours on a week on a charger.
Driving across Europe on your summer hols is the corner case, Lidl/school runs are the vast majority of trips.
It used to be that evaporation from petrol tanks emitted more hydrocarbons than came unburnt out of the exhaust. But evaporation controls have been getting increasingly elaborate for some decades. My older model has a one-way valve in the fuel cap to let air in as the tank empties and a vent pipe which goes via a canister of charcoal granules to absorb fumes, and that gets air drawn back through it while the car's cruising to scavenge fumes and feed them into the engine. Later ones like yours I think draw a small partial vacuum on the fuel tank and check it's maintained. The US model does anyway: it warns you if you failed to tighten the petrol cap.shpalman wrote: ↑Wed Jan 12, 2022 9:07 am...
My ~20 year old sports car achieved about 6.6 l/100km (35.6 mpg(US), 42.8 mpg(UK), 0.066 mm2) on my trip to Slovakia and back (to Italy) including however much evaporated in the two weeks it was parked in Slovakia hardly going anywhere. Normally I get somewhere between 8 and 10 l/100km. Note that I don't have a fuel consumption gauge or anything, this is based on how many km I did and how many litres I filled up with, so also includes the angel's share.
I certainly notice the small partial vacuum when I take the cap off to fill the tank. The petrol cap clicks as you tighten it.Martin Y wrote: ↑Wed Jan 12, 2022 10:44 amIt used to be that evaporation from petrol tanks emitted more hydrocarbons than came unburnt out of the exhaust. But evaporation controls have been getting increasingly elaborate for some decades. My older model has a one-way valve in the fuel cap to let air in as the tank empties and a vent pipe which goes via a canister of charcoal granules to absorb fumes, and that gets air drawn back through it while the car's cruising to scavenge fumes and feed them into the engine. Later ones like yours I think draw a small partial vacuum on the fuel tank and check it's maintained. The US model does anyway: it warns you if you failed to tighten the petrol cap.shpalman wrote: ↑Wed Jan 12, 2022 9:07 am...
My ~20 year old sports car achieved about 6.6 l/100km (35.6 mpg(US), 42.8 mpg(UK), 0.066 mm2) on my trip to Slovakia and back (to Italy) including however much evaporated in the two weeks it was parked in Slovakia hardly going anywhere. Normally I get somewhere between 8 and 10 l/100km. Note that I don't have a fuel consumption gauge or anything, this is based on how many km I did and how many litres I filled up with, so also includes the angel's share.
That's going to be true for anything with lithium ion batteries. And drawing the power from cold batteries to provide that heat to the batteries at the same time as driving is inefficient.
This isn't quite true - as mentioned above for the Prius. Regen isnt effective at braking a vehicle below ~7mph, so stop start traffic results in the traditional brakes being used.lpm wrote: ↑Wed Jan 12, 2022 8:59 amEVs have a different profile to ICE. They do best in slow city travel because they just regen any slowing. They enjoy a nice traffic jam on the motorway but can't defeat drag at 70 mph.Martin_B wrote: ↑Wed Jan 12, 2022 12:58 amI find that driving around Perth on roads with 60-80 km/h speed limits I can usually get ~6 litres/100 km (sorry, that's the way my car reports it!).
But when doing long drives on roads with higher speed limits (between 100 km/h and 130 km/h) I could get down to 4.5 litres/100 km quite easily. I'm not sure lpm's idea:is accurate, as on motorways you do drive faster and so have more drag, but you also tend to drive more consistently and so have fewer accelerations and decelerations. (Oz highways may be different to UK motorways, though!)
I'm almost certain that most or all hybrid cars you can buy are parallel hybrids not series hybrids, in other words both the engine and the electric motor-generator drive the wheels through a mechanical transmission. Otherwise you'd need a bigger motor to deliver the full engine power and an equally big generator to convert the engine's power to electricity to run the big motor. I know that works for diesel-electric trains, but guess the numbers don't make sense for a car. Some hybrids (e.g. Toyotas) use a continuously variable transmission to keep the engine at an optimum speed, but others just have a more conventional automatic gearbox.IvanV wrote: ↑Wed Jan 12, 2022 9:35 amIt is one reason that you get surprisingly good fuel efficiency out of a system where petrol engine charges a battery, and the wheels are moved by electric motors. (What is marketed as a self-charging hybrid, trying to distract from the fact that it runs entirely on petrol). Despite the losses in charging the battery, you get a benefit from being able always to run the engine at it's efficient sweet spot, which, depending on kind of journeys you drive, can result in lower fuel consumption. (But why they don't go the small step further and let you plug them in is beyond me, given most journeys are short. Can it really add that much extra to the cost of the vehicle?)
There'll be some baseline power consumption that starts to dominate at very slow speeds, but I would guess the optimum will be much slower than anyone would want to go.
This is only true while the drag coefficient remains constant. But as speed changes, there drag coefficient can reduce (or increase) substantially.
I don't believe that's the case for full EVs. They don't use the friction brakes at all, except in emergency stops or very hard braking. This is why there's a trend towards one pedal driving like for Nissan Leaves.
The electric range of plugin hybrids seems to be fairly well chosen to cover completely day to day short urban journeys, and only needing the ICE for journeys long enough to be on a highway at constant high speed. That matches up pretty well to the efficiencies of each part of the system, as extra weight is less of an issue for efficiency in highway driving.nekomatic wrote: ↑Wed Jan 12, 2022 12:41 pmI'm almost certain that most or all hybrid cars you can buy are parallel hybrids not series hybrids, in other words both the engine and the electric motor-generator drive the wheels through a mechanical transmission. Otherwise you'd need a bigger motor to deliver the full engine power and an equally big generator to convert the engine's power to electricity to run the big motor. I know that works for diesel-electric trains, but guess the numbers don't make sense for a car. Some hybrids (e.g. Toyotas) use a continuously variable transmission to keep the engine at an optimum speed, but others just have a more conventional automatic gearbox.IvanV wrote: ↑Wed Jan 12, 2022 9:35 amIt is one reason that you get surprisingly good fuel efficiency out of a system where petrol engine charges a battery, and the wheels are moved by electric motors. (What is marketed as a self-charging hybrid, trying to distract from the fact that it runs entirely on petrol). Despite the losses in charging the battery, you get a benefit from being able always to run the engine at it's efficient sweet spot, which, depending on kind of journeys you drive, can result in lower fuel consumption. (But why they don't go the small step further and let you plug them in is beyond me, given most journeys are short. Can it really add that much extra to the cost of the vehicle?)
The battery in a non-plugin hybrid really isn't big enough to get the car very far (or very fast, given it's not sized for the full engine power) so no, I don't think it would make sense to add the cost of being able to plug it in. The issue with plugin hybrids is that once you make the battery big enough to have a usable electric range, the extra weight means that after you use up the electric range the car can end up using more fuel for subsequent driving than its non-hybrid equivalent.
I'd expect it to be true at some level for holding the vehicle still on hills when stopped - a stationary motor only provides significant torque to resist movement if it's powered and dissipating energy, which is inefficient.
I hope someone hacks it and makes everyone's cars sound like crazy frog.dyqik wrote: ↑Wed Jan 12, 2022 8:13 pmCustom exhausts for your EV:
https://www.millteksport.com/active-sou ... ta105.html
That was tried in the USA in 1973 - though the way it was expressed was as a measure to save fuel which is obviously exactly the same thing as reducing emissions. I haven't seen any evidence which says how much, if an, was saved.Bird on a Fire wrote: ↑Wed Jan 12, 2022 12:24 amI've even seen suggestions of lowering the speed limit to reduce CO2 emissions.
I think your right. The Vauxhall one (Ampex?) and the I3 Rex were series hyibrids, although the Rex (in initial version at least) only had about 2 teacups of petrol for some California incentive reason.Ivan: I'm almost certain that most or all hybrid cars you can buy are parallel hybrids not series hybrids
I usually need to pee and eat several times on such a journey.
From Como, I stopped for lunch in Bregenz, stopped overnight near Munich, and stopped for lunch the next day in St. Pölten but that was a waste of time because it was Sunday. I'll have to choose a more interesting lunch stop next time, maybe somewhere on the edge of Vienna (I actually ended up driving past the Schönbrunn on the way back because of an autobahn tunnel closure, and ate sandwiches at a rest stop).
The incentive, I gather, was to get a green sticker which let you drive in carpool lanes with only one person aboard.